There have been attempts to fabricate flexible elements and components based on printed electronics technology, and printed electronics is increasingly used, mostly in product ranges such as displays, RFID, and solar power. In printed electronics, printing usually occurs at a lower temperature than a semiconductor process or at room temperature. Elements are fabricated by a coating process, a printing process, a patterning process, etc., and flexible components can be made via a post-process for forming wiring and electrodes and processes like joining and cutting.
In the actual fabrication of devices using elements, space for wiring and other uses is needed. That is, space is needed between each device, but cannot be formed if all elements arranged on a wafer are transferred at once, which makes device fabrication difficult.
Moreover, for a device consisting not of a single type of element but of multiple types of elements, one element is transferred first, and then another element is transferred near it. As can be seen from this example, a transfer process for device fabrication often requires a process of selectively transferring an element, and there is an already known technique for selective transfer using a patterned stamp in the transfer process.
FIG. 1 is a view showing an example of a conventional selective transfer roll stamp, and FIG. 2 is an enlarged view of protrusions on the selective transfer roll stamp of FIG. 1.
Referring to FIG. 1 and FIG. 2, the conventional selective transfer roll stamp includes a roller 20 rotating about the axis of rotation, and an adhesive layer 30 covering the roller 20. Protrusions 31 are formed on the surface of the adhesive layer 30, and flat portions 32 are formed between neighboring protrusions 31. A plurality of elements 1 arranged on a source substrate 10 are separated from the source substrate 10 as they are attached to the protrusions 31 on the rotating stamp.
However, as shown in FIG. 2, in a case where a contact load F is applied in the process of transferring elements 1 on the source substrate 10 to the stamp, the flat portions 32, as well as the protrusions 31 on the stamp, may collapse, leading to the risk of bringing the flat portions 32 into contact with the elements 1 on the source substrate 10. In that case, the elements 1 are transferred to the stamp, which should not happen, and this makes the whole process defective.
As the size and pitch of the protrusions 31 become smaller, the flat portions 32 collapse more frequently, especially when transferring micro-sized elements 1, thus leading to a further decrease in process defect rates.
Moreover, the conventional selective transfer roll stamp should be replaced often because the protrusions wear out or become damaged over a long-time process.